Method for plating semiconductor chip headers

ABSTRACT

A method and apparatus for selectively plating the die-attach area of a semiconductor chip header are described. The apparatus comprises a rotary disc assembly. In the assembly there is provided a plurality of cavities for removably receiving individual headers. In each cavity there is provided an annular masking member for masking a header situated therein. Associated with each cavity, there is provided a cam-operated clamping means for clamping a header against the masking member and for coupling a source of potential to the header. Also associated with each cavity is a fluid jet for jetting a plating fluid against the header through a hole in the center of the sealing member. Plating fluid is selectively pumped, by means of a pumping means, to each of the jets along a plurality of fluid passageways from a fluid manifold. The fluid manifold is adapted to couple a predetermined number of the fluid passageways and jets to the pumping means as the disc assembly is rotated. Means are also provided for automatically releasing the clamping means and removing each header from the apparatus after completion of the plating operation.

This is a division of application Ser. No. 619,368 filed October 3,1975, now U.S. Pat. No. 4,032,422.

BACKGROUND OF THE INVENTION

The present invention is related to a method and apparatus for platingsemiconductor chip headers in general and, in particular, to a methodand apparatus for selectively plating the die-attach area of a headeronly.

The plating of the die-attach area of a semiconductor chip headertypically requires the use of a precious metal, such as gold. In spiteof the fact that the die-attach area extends over but a limited area ofthe top of a header, it has been the practice heretofore, to plate theentire header or at least a substantial part of its top and sides. Sinceonly the die-attach area need be plated to satisfy currentstate-of-the-art technology, an obvious savings in precious metals isobtainable by restricting the use of such metals to that area.

SUMMARY OF THE INVENTION

In view of the foregoing, principal objects of the present invention area method and apparatus for selectively plating the die-attach area of asemiconductor chip header.

In the apparatus there is provided a rotary disc assembly. In the uppersurface of the assembly, there is provided a plurality of headerreceiving cavities. In each of the cavities there is provided an annularsealing member. Associated with each of the cavities is a cam-operatedclamping member. The clamping member is provided for clamping a headerin the cavity, coupling a source of potential between the header and afluid jet associated therewith, and pressing the header against thesealing member. Centered relative to the hole in each of the sealingmembers is a fluid jet. Fluid for each of the jets is provided through aplurality of fluid passageways which extend radially from the center ofthe disc assembly. In the center of the disc assembly, there is provideda stationary fluid manifold. The manifold acts as a fluid valve and isadapted to connect a predetermined number of the fluid passageways to asource of plating fluid under pressure as the disc assembly is rotated.Means are also provided for automatically removing plated units from theholes so that the apparatus is usable in continuous plating operations.pg,3

DESCRIPTION OF THE DRAWINGS

The above and other objects of the present invention will becomeapparent upon a reading of the following detailed description of theaccompanying drawings in which:

FIG. 1 is a partial perspective view of an apparatus according to thepresent invention.

FIG. 1A is a partial perspective view of a portion of the electricalcircuit of the apparatus of FIG. 1.

FIG. 1B is a plan view of FIG. 1A.

FIG. 2 is an elevation view taken along lines 2--2 of FIG. 1.

FIG. 3 is a transverse cross-sectional view of the apparatus of FIG. 2.

FIG. 4 is an elevation view of one of the clamping assemblies of thepresent invention.

FIG. 5 is a cross-sectional view showing the position of the clamp ofFIG. 4 relative to a header being plated.

FIG. 6 is an elevation view showing a header after release of the clampof FIG. 5.

FIG. 7 is a plan view of a fluid manifold according to the presentinvention.

FIG. 8 is a side view of FIG. 7.

FIG. 9 is a plan view of one of the disc members of a rotary discassembly according to the present invention.

FIG. 10 is a cross-sectional view of the member of FIG. 9.

FIG. 11 is plan view of another of the disc members of the rotary discassembly according to the present invention.

FIG. 12 is a cross-sectional view of the member of FIG. 11.

DETAILED DESCRIPTION

Referring to FIG. 1, there is provided in accordance with the presentinvention, a rotary disc assembly 1 mounted for rotation on a table 2.Table 2 is provided with a plurality of sidewalls 3, 4, 5 and 6, a topwall 7 and a pair of leg members 8 and 9. Leg members 8 and 9 areprovided for supporting assembly 1 above a floor table or othersupporting surface.

In assembly 1, there is provided a first circular disc member 10 havinga plurality of cylindrical header- receiving cavities 11. Cavities 11are equidistantly spaced apart and typically lie along a circular linenear the periphery of the disc member. Interior of the cavities 11,there is provided a circular electrically conductive ring 12. In slidingcontact with the ring 12 is an electrical contact 14. Contact 14 isadapted for coupling the ring 12, as by a wire 13, to the negative poleof a d.c. current source, such as a battery B. Pivotably mounted tomember 10 between ring 12 and each of the cavities 11 is a spring-biasedovercenter header clamping assembly 20, only one of which is shown. Eachof the clamping assemblies 20 is electrically connected to the ring 12as by a wire or the like 21.

In the center of assembly 1 is a spindle 22. Extending from the top ofspindle 22 is a shaft 23. On shaft 23 there is provided an electricallyconductive plate or pad 24 which is electrically connected to thepositive pole of the source B as by a wire 25.

To the right of spindle 22, as shown in FIG. 1, and supported abovemember 10 as by a supporting rod 26 is a first camming member 27. To theleft of spindle 22 and supported about the axis of a shaft 28 is amagnetic wheel or disc 29. Mounted on the shaft 28 below disc 29 is aroller 30. Roller 30 is driven by the disc member 10 for rotating themagnetic disc 29.

Referring to FIGS. 1A and 1B, the wire 25, coupled to source B, iselectrically connected to the pad 24 mounted on shaft 23 as by a slidingcontact 31. Pad 24 extends about the circumference of the shaft 23 for apredetermined distance for selectively electrically connecting anddisconnecting the source B to and from a predetermined number of theclamping assemblies 20 of the assembly 1 as the shaft 23 is rotated.

Referring to FIG. 2, there is also supported above the disc member 10 asby a shaft 35, a second camming member 36. While omitted from FIGS. 1and 2, it is understood that the upper end of the shafts 23, 26, 28 and35 are supported in any suitable manner by an overhead supportingchannel or the like; shafts 23 and 28 being rotatably supported suchthat shafts 23 and 28 are free to rotate and shafts 26 and 35 beingfixedly supported such that members 27 and 36 are held in a stationaryposition relative to the member 10 as the member 10 is rotated.

Referring to FIG. 3, there is further provided in table 2, a bottom wall37. Walls 3, 4, 5 and 6, described above with respect to FIG. 1, andwall 37 are joined in a fluid-tight manner for containing a platingfluid within a volume 40.

Above wall 37 and immediately adjacent to and below the first discmember 10 is a second disc member 41. Immediately adjacent to and belowthe second disc member 41 is a third disc member 42. For supporting thedisc members 10, 41 and 42, spindle 22 is provided with a radiallyextending shoulder 43. Below spindle 22 and underlying shoulder 43 thereis provided an annular ring-shaped member 44 supported on acylindrically- shaped supporting member 45. Member 45 is supported onthe bottom wall 37. Concentric with shaft 23, there is provided abushing 46.

Referring to FIGS. 11 and 12, there is provided in each of the cavities11 in disc member 10 a hole 50 having a diameter which is smaller thanthe diameter of the cavities. In the underside of the member 10 andextending about its periphery is a shoulder 51. Extending downwardlyfrom the shoulder 51 at the interior edge thereof is a member forforming a fluid splash guard 52. The shoulder 51 is provided to extendover the top wall 7 and the member 52 is provided to extend beneath thewall 7. In the center of the disc member 10 there is provided a bore 53for receiving the spindle 22.

Referring to FIGS. 9 and 10, there is provided in the upper surface andextending about the periphery of second disc member 41, a shoulder 60.Fixed to the surface of shoulder 60 is an electrically conductive strip61. Spaced about and extending through shoulder 60 and strip 61 forregistration with holes 11 and 50 of first disc member 10 are aplurality of holes 62.

In third disc member 42 and extending radially in the upper surfacethereof there is provided a plurality of elongated cavities 70. Each ofthe cavities 70 is terminated at its outer end by an enlarged area 71.Each of the areas 71 is provided for registration with the holes 11 and50 of first disc member 10 and the holes 62 of second disc member 41. Atthe interior end of each of cavities 70, there is provided a hole 72. Inthe shouldered portion 43 of spindle 22 there is provided forregistration with each of the holes 72, a hole 80. In the center of eachof the second and third disc members 41 and 42, there is furtherprovided a spindle-receiving bore for receiving the spindle 22 suchthat, when second disc member 41 is placed on top of third disc member42 and holes 72 placed in registration with holes 80 and enlarged areas71 placed in registration with holes 62, there is formed a plurality ofradially extending fluid passageways 90, each of which extends from thelower end of one of the holes 80 to the upper end of one of the holes62.

Referring to FIGS. 7 and 8, there is provided in annular member 44 acavity 91. In the base of cavity 91 there is provided, extending throughthe member 44, a hole 92. In the center of member 44, there is provideda bore 93 for receiving the spindle 22.

Referring again to FIG. 3, as previously described, member 44 issupported by the cylindrical supporting member 45. In the top of thebody of member 45 is a recess for receiving the member 44 such that theupper surface of member 44 serves as a bearing surface for the spindle22. Extending from the recess in the body of member 45, and positionedfor registration with hole 92 of member 44, there is provided a hole 93.Extending from the hole 93 is another hole 94. Coupled to the hole 94 asby a pipe or the like 95, is the output of a fluid pump 96. The input ofthe pump 96 is coupled directly, or by means of a pipe or the like 97,to the volume 40 for pumping fluid from the volume.

Referring to the second disc member 41, as shown in FIG. 3, and to FIGS.5 and 6, there is provided in each of the holes 62 a fluid jet 100having an extended nozzle member 101. The lower end of jets 100 istypically screwed into the holes 62 such that the jet makes electricalcontact with the strip 61. The strip 61 and hence each of the jets 100are electrically coupled, as by a wire or the like 102, to the pad 24 onthe shaft 23. The wire 102 typically runs from the strip 61 between thefirst and second disc members 10 and 41, along the outside of thespindle 22 and up the shaft 23 to the pad 24.

As shown in FIGS. 5 and 6, there is provided in each of the cavities 11of first disc member 10, an annular resilient member 103 having acentral hole 104. Member 103 is provided for masking off the die-attacharea of a semiconductor chip header 105 when the header is pressed topdown against the member. The top of the nozzle portion 101 of each ofthe jets 100 is provided to extend through the holes 50 of first discmember 10 and into the center hole 104 of the members 103.

In each of the clamping assemblies 20 associated with one of thecavities 11 first mentioned above with respect to FIG. 1, there isprovided a vertically extending body member 110. Extending outwardlyfrom and perpendicularly to the lower end of member 20 is a pair ofspaced leg members 111 and 112. At the top of member 110 and rotatablyattached thereto for rotation about a pin or the like 113 is a roller114. Each of the assemblies 20 is pivotably attached to the first discmember 10 by means of a pair of spaced upstanding members 115 and 116.On opposite sides of member 110 there is provided a pair of springmembers 117 and 118. Members 117 and 118 are attached at their top endsto the member 110 and at their bottom ends to the members 115 and 116such that they function as an overcenter clamping assembly when pivotedbetween a first position, as shown in FIG. 4, and a second position, asshown in FIG. 5.

In operation, a plurality of headers, such as that represented by header105 in FIGS. 5 and 6, are placed by hand or in any other suitablemanner, in the cavities 11 of the first disc member 10. In practice,this is done while the assembly 1 is being rotated in acounter-clockwise direction looking from the top, as by a motor or thelike (not shown) coupled to either end of the shaft 23. As the rollers114 contact the first camming member 27, the clamping assemblies 20 areurged forwardly causing the leg members 111 and 112 to engage the top ofa header, as shown in FIGS. 2 and 5, pressing the top of the headeragainst the resilient masking member 103. At the same time, platingfluid which is placed intitially in the volume 40, is being pumped bypump 96 through the pipe 95, passageway 93 and hole 92 into the cavity91 of annular member 44. Also at the same time, the electricallyconductive pad 24 on shaft 23 is being rotated toward the electricalcontact 31. At a predetermined time, after each of the headers is firmlypressed against its sealing member 103, and the spring members 117 and118 of its overcenter clamping assembly 20 are positioned to hold theheader in a fluid-tight seal therewith, the hole 80 in the lower end ofthe spindle 22 at the end of the passageway 90 associated with theheader overrides the cavity 91 in member 44 and comes into fluidcommunication therewith. Simultaneously the electric contact 31 comesinto sliding contact with electrical pad 24 such that there is thenprovided an electric field between the header and its associated fluidjet 100. As fluid flows from the cavity 91, through passageway 90 andits jet 100, a current flows in the fluid being jetted against theheader, causing a plating metal to deposit on the unmasked surface ofthe header. The plating operation thus initiated continues as theassembly 1 is rotated until the contact 31 leaves the pad 24 and/or thehole 80 in the bottom of spindle 22 ceases to be in fluid communicationwith the cavity 91 in member 44.

Thereafter, the roller 114 comes into contact with the second cammingmember 36 and is urged rearwardly, releasing the header. As the assembly1 continues to rotate, the leads of the header are contacted by themagnetic disc member 29 and the header removed. By any suitable means(not shown), the header is scraped or otherwise removed from the discmember 29 and deposited in a bin or the like for further processing.

Referring again to FIGS. 7 and 9, it can be seen that in the embodimentof member 44 described hereinabove, the length of cavity 91 is such thatthe cavity subtends an arc of approximately 90° and that at least fiveof the passageways 90 fall within the same angular displacement. It is,therefore, apparent that plating fluid is being jetted against at leastfive headers at all times and that more or less than that number can beplated simultaneously by adjusting the arc length of the cavity 91. Ifany change in the length of cavity 91 is made, however, a correspondingadjustment in the size and position of the electrical pad 24 relative tothe electrical contact 31 may also be required.

It may be noted at this point that the switching of the source B bymeans of the use of pad 24 is simply for purposes of safety and that, ifsafety is not a consideration, the pad could be continuous and theswitching of the source B eliminated.

As is conventional in most plating apparatus, the parts which come intocontact with plating fluid are fabricated from well known materialswhich are compatible with the fluid such that the apparatus is notcorroded and the fluid is free from contamination such as, for example,platinum for the electrical parts and any of several non-metallicmaterials for the non-electrical parts.

While a specific embodiment is described, it is understood that variouschanges and modifications in details and arrangements of the parts maybe made within the spirit and scope of the present invention.Accordingly, it is intended that the scope of the invention be notlimited to the embodiment described, but rather be determined accordingto the claims and their equivalents hereinafter provided.

What is claimed is:
 1. A method of plating the die-attach area of aplurality of semiconductor chip headers comprising the steps of:placingeach of said headers in an inverted position against a sealing member ina cavity of a rotating disc assembly; clamping said headers against saidsealing member such that said sealing member forms a fluid-tight sealabout said die-attach area; jetting a plating solution containing aplating material against said exposed areas; and causing a current toflow through said headers while said solution is being jetted againstsaid exposed areas whereby plating material in said solution adheres tosaid exposed area; wherein said step of jetting comprises the step ofjetting said solution against said die-attach area after said clampingof said headers and further wherein said step of causing a current toflow comprises the step of coupling a source of potential between ameans for clamping said headers and a means for jetting said fluidagainst said die-attach areas such that said current will flow when saidheaders are contacted by said clamping means and said plating solutionis flowing between said jetting means and said die-attach areas.
 2. Amethod according to claim 1 wherein said step of clamping comprises thestep of clamping said headers by means of a cam-operated pivotableover-center clamping means associated with each of said cavities.
 3. Amethod according to claim 2 wherein said step of clamping said headerscomprises the step of clamping said headers during a predeterminedportion of each revolution of said rotating disc assembly and furtherwherein said step of jetting plating solution against said die-attachareas comprises the step of jetting said plating solution against saiddie-attach areas during said predetermined portion of each revolution ofsaid rotating disc assembly.